Clarification of ammonium polyphosphate solutions

ABSTRACT

Suspended black carbonaceous material contained in aqueous ammonium polyphosphate solutions, which are derived from impure wet-process phosphoric acid, is removed by mixing such a solution with ionic, water soluble, high polymers having a molecular weight in excess of one million, holding the mixture until the suspended material flocculates and floats to the surface, and separating the flocculated carbonaceous material from the resulting clarified ammonium polyphosphate solution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.781,625, filed Mar. 28, 1977 now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to the removal of particulate matter fromammonium polyphosphate solutions which are prepared from impurewet-process phosphoric acid. More particularly, it relates to a new andimproved process for the flocculation, flotation, and removal ofsuspended, black, carbonaceous impurities from aqueous solutions ofammonium polyphosphate which are produced from wet-process phosphoricacid.

Wet-process phosphoric acid is produced by the reaction of phosphaterock, particularly calcium phosphate, with sulfuric acid and separatingthe resulting crude phosphoric acid from the precipitated calciumsulfate and other insoluble materials. This crude acid ordinarilycontains about 30 to 32% P₂ O₅ when produced (filter-grade acid) and isnormally concentrated to a P₂ O₅ concentration of about 52 to 54%(merchant-grade acid) before shipment. Concentration of the wet-processacid prior to shipment not only serves to increase the P₂ O₅ content,but also has the effect of increasing the concentration of impuritiesthat are present.

Crude wet-process phosphoric acid contains varying amounts of impuritiessuch as iron, aluminum, calcium, magnesium, and other metals in the formof their phosphates, sulfates, or fluorides, depending on thecharacteristics of the specific phosphate rock which is used as thestarting material. In addition to these inorganic impurities, organicmaterials are also commonly present as contaminants and are derived fromorganic substances originally present in the phosphate rock and fromorganic chemicals utilized in benefication of the rock prior totreatment with sulfuric acid. A portion of these impurities are in solidform and result from imperfect filtration, from precipitation duringconcentration, or from post-precipitation. Other impurities are solubleand remain in solution.

Phosphate rock which is utilized for the preparation of a wet-processphosphoric acid is often heavily contaminated with both soluble andinsoluble organic material. Although organic material can be removed bycalcination of the phosphate rock prior to use, such processing isbecoming increasingly unfeasible as a result of the large energyrequirement involved. This is illustrated by the fact that suchcalcination requires an expenditure of about 3 million Btu per ton ofrock. Consequently, furnace-grade phosphoric acid, which is preparedfrom calcined phosphate rock, is becoming increasingly expensive andimpractical for use in applications such as the preparation offertilizers.

In the preparation of liquid fertilizers, it has been found desirable toconcentrate merchant-grade phosphoric acid to higher P₂ O₅ values. Bysubjecting the merchant-grade acid to evaporating means, either atatmospheric or reduced pressure, the P₂ O₅ content can be increased fromabout 52 to 54% to a value in the range from about 60 to 76%. Thisconcentration results in a molecular dehydration of the phosphoric acidand conversion from the orthophosphate form to the polyphosphate form.Occurring concurrently with the molecular dehydration of themerchant-grade acid is the charring of dissolved organic impurities atthe elevated temperatures required. The resulting product is a blackphosphoric acid solution which contains a substantial amount ofpolyphosphate and also a plethora of suspended, black carbonaceousparticles which originate from the organic impurities in themerchant-grade starting material. Although it would be highlyadvantageous to clarify this black phosphoric acid before itscombination with other components, as in the manufacture of fertilizersolutions, no practicable process for doing this has yet been devised.

Wet-process phosphoric acid is widely used in the manufacture ofammonium polyphosphate fertilizer solutions. Two basic methods areutilized for this purpose. One method, as set forth in U.S. Pat. No.3,044,851, involves the dehydration of merchant-grade wet-processphosphoric acid followed by reaction with ammonia in a subsequent step.Alternatively, as set forth in U.S. Pat. No. 3,382,059, filter-grade ormerchant-grade wet-process phosphoric acid can be reacted with anhydrousammonia, and the autogenous heat of reaction utilized to dehydrate andconvert the orthophosphate starting material to ammonium polyphosphatein a single step. Unfortunately, both of these methods produce ammoniumpolyphosphate solutions which are highly discolored due to the presenceof black carbonaceous particular matter. This particulate carbonaceousmaterial is derived from organic impurities in the wet-processphosphoric acid which char and are rendered insoluble during thedehydration which converts the orthophosphate starting material to apolyphosphate product. Although furnace-grade phosphoric acid can beutilized, in place of the wet-process material, to produce clearammonium polyphosphate solutions which are free of black, particulatecarbonaceous material, a substantial economic penalty accompanies theuse of furnace-grade acid.

Liquid fertilizers having compositions similar to those of standard drymixed fertilizers are well known in the industry and are increasing inpopularity. Such solutions are superior to dry mixed fertilizers in thatthe cost of evaporating water and bagging the product are eliminated andsoil application is greatly simplified. In addition, the use of liquidfertilizers eliminates difficulties due to segregation and caking whichare often encountered in the storage of dry fertilizers. Althoughammonium polyphosphate solutions prepared from wet-process phosphoricacid, as detailed supra, are currently the preferred source of liquidfertilizers containing nitrogen and phosphorus, they suffer from theserious deficiency of an inky black color which is due to suspended,black carbonaceous particulate matter. Filtration of the black ammoniumpolyphosphate solution is not practicable since the carbonaceousparticles coalesce on the filter to generate a sticky impermeable layerwhich prevents further filtration. In addition, this suspendedcarbonaceous material will not spontaneously settle under conditionswhich would permit its removal on a large scale.

Black ammonium polyphosphate fertilizer solutions, which are preparedfrom wet-process phosphoric acid, are objectionable since the darkcoloration masks the presence of precipitated solids which can result inplugged equipment and difficulties in the application of such materialto the soil. In addition, this type of black fertilizer solution is lessaesthetically pleasing than a clear ammonium polyphosphate solutionwhich does not contain suspended black carbonaceous material, but whichis otherwise the same. In view of these factors, consumers are becomingincreasingly resistant to the use of black ammonium polyphosphatefertilizer solutions or other black fertilizer solutions derived fromthem. At the present time, the consumer will not use these black liquidsexcept in the case of extreme emergency. Consequently, a large pricedifferential exists between the black ammonium polyphosphate solutionsand clear green solutions of the same analysis.

It has previously been demonstrated that suspended, black carbonaceousmaterial can be removed from aqueous ammonium polyphosphate solutions bya flocculation and flotation process. U.S. Pat. No. 3,630,711, isdirected to a method for clarifying black 10-34-0 grade ammoniumpolyphosphate solutions. This method involves the addition of from about0.1 to about 0.6% by weight of a water insoluble aliphatic amine to theblack solution followed by vigorous agitation of the mixture after whichthe carbonaceous material is permitted to flocculate and float tosurface as a froth. The resulting froth is then conveniently removed.

An improved flocculation and flotation process for the clarification ofblack, aqueous ammonium polyphosphate solutions is set forth in U.S.Pat. No. 3,969,483. This improved process involves the combination oftwo flocculating agents, one of which is either an aliphatic amine or analiphatic amine acetate and the other is a quaternary ammonium chloride.These two flocculating agents act together in a synergistic manner andproduce flocculation at addition rates which are significantly lowerthan those required by the process disclosed in U.S. Pat. No. 3,630,711.Even with this improved process, however, it is still necessary to use atotal of about 0.1% of these two flocculating agents in order to producea clear ammonium polyphosphate solution having a light absorbance below0.3 (relative to distilled water at 560 nm). This process also requiresvigorous agitation of the mixture of black ammonium polyphosphatesolution and flocculating agents. In addition, this process is carriedout at elevated temperatures in the range from about 165° to about 190°F. which results in the substantial and undesirable loss ofpolyphosphate content in the solution.

It is an objective of this invention to prepare from wet-processphosphoric acid, a clear aqueous solution of ammonium polyphosphatewhich is essentially free of suspended, black carbonaceous material.

Another objective of this invention is to provide a process for theclarification of black ammonium polyphosphate solutions which arederived from wet-process phosphoric acid, which process which can becarried out at lower temperatures than has been heretofore possible.

A further objective of this invention is to provide a process for theclarification of black ammonium polyphosphate solutions which arederived from wet-process phosphoric acid, which process does not requirevigorous agitation of a flocculating agent with the black solution.

A still further objective of this invention is to provide a new and moreeffective agent for the clarification of black ammonium polyphosphatesolutions which are prepared from wet-process phosphoric acid.

SUMMARY OF THE INVENTION

The present invention is directed to a process for the flocculation andremoval of suspended, finely divided, insoluble, carbonaceous materialfrom aqueous ammonium polyphosphate solutions, derived from wet-processphosphoric acid, which comprises the steps of:

(a) mixing said ammonium polyphosphate solution with an aqueous solutionof at least one ionized, water soluble, organic high polymer having amolecular weight in excess of one million, wherein said organic polymeror polymers are either cationic or anionic materials, wherein the amountof said polymer is from about 0.001 to about 0.5% by weight based on theweight of said ammonium polyphosphate solution, and wherein said aqueousorganic polymer solution contains from about 0.1 to about 5% by weightof said organic polymer;

(b) holding the resulting mixture for a period of time effective topermit the separation of said mixture into an upper layer of flocculatedcarbonaceous material and a lower layer of clarified ammoniumpolyphosphate solution; and

(c) separating said lower layer of clarified ammonium polyphosphatesolution from said upper layer of flocculated carbonaceous material.

Step (a) of the above described process can also be advantageouslycarried out by using a combination of cationic and anionic organic highpolymers according to either of the following modifications:

1. Sequentially adding to the unclarified ammonium polyphosphatesolution from about 0.001 to about 0.5% of at least one cationic organicpolymer followed by from about 0.001 to about 0.1% of at least oneanionic organic polymer; wherein said percentages are by weight and arebased on the weight of said ammonium polyphosphate solution; whereinsaid organic polymers are water soluble and have a molecular weight inexcess of one million; and wherein the organic polymers are added in theform of aqueous solutions which contain from about 0.1 to about 5% byweight of polymer.

2. Sequentially adding to the unclarified ammonium polyphosphatesolution from about 0.001 to about 0.5% of at least one anionic organicpolymer followed by from about 0.001 to about 0.1% of at least onecationic organic polymer; wherein said percentages are by weight and arebased on the weight of said ammonium polyphosphate solution; whereinsaid organic polymers are water soluble and have a molecular weight inexcess of one million; and wherein the organic polymers are added in theform of aqueous solutions which contain from about 0.1 to about 5% byweight of polymer.

DETAILED DESCRIPTION OF THE INVENTION

This invention is an improved process for the separation of suspended,insoluble, black, carbonaceous material from ammonium polyphosphatesolutions which are produced from wet-process phosphoric acid. Thewet-process phosphoric acid used to prepare these ammonium polyphosphatesolutions may contain from about 30 to about 76% P₂ O₅. The ammoniumpolyphosphate solutions are then produced by the molecular dehydrationand subsequent or concurrent ammoniation of this wet-process phosphoricacid. These ammonium polyphosphate solutions have a pH above about 4.5and, preferably, above about 5.0. In addition, the ammoniumpolyphosphate solutions contain from about 10 to about 90% by weightand, preferably, from about 50 to about 90% by weight of the total P₂ O₅in a polyphosphate form. Preferred solutions contain a nitrogen contentof about 8 to about 13% and a P₂ O₅ content of about 27 to about 37%.Consequently, the preferred ammonium polyphosphate solutions range ingrade from about 8-27-0 to about 13-37-0. Most preferably, the ammoniumpolyphosphate solution is of about a 10-34-0 grade.

The separation of suspended, insoluble, carbonaceous material from theammonium polyphosphate solutions is accomplished by mixing such asolution with a small amount of an organic, polymeric, ionic flocculant,allowing the carbonaceous material to coagulate and float to thesurface, and then drawing off the bottom layer of clarified ammoniumpolyphosphate solution. Only certain specific flocculants are suitable,however, and these are all ionic, water soluble, organic high polymershaving molecular weights in excess of one million. Either anionic orcationic organic polymers can be used, but the cationic polymers arepreferred. Nonionic organic polymers are unsatisfactory and cannot beused as flocculants in the process of this invention.

The ionic organic polymers of this invention, preferably, possess a highcharge density. At concentrations of 1 to 2% in water, these ionicorganic polymers produce solutions having viscosities greater than about400 centipoise at ambient temperatures. The polymers must be dissolvedin water prior to use, and preferably, the aqueous solution is allowedto stand for a period of at least about one hour prior to use. Duringthis standing period, it is believed that the polymer molecules areconverted from a coiled to an extended configuration in which form theyare most effective in flocculating the suspended carbonaceous material.

As a result of the high viscosity of aqueous solutions of the ionicorganic high polymers of this invention, it is virtually impossible tohandle solutions having a concentration greater than about 5%, anddifficult to handle solutions having a concentration greater than about2% by weight. Since, however, water in the polymer solution serves todilute the final clarified ammonium polyphosphate solution, it isdesirable to use the polymer in the form of an aqueous solution which isas concentrated as possible. Consequently, it is highly preferred to usean aqueous solution containing from about 1 to about 2% by weight of theionic organic polymer. Nevertheless, the process of this invention maybe carried out using an aqueous solution which contains from about 0.1to about 5% by weight of ionic organic polymer.

Satisfactory organic, polymer ionic flocculants for use in the processof this invention includes the following specific materials:

Primafloc C-3, a cationic flocculant, a condensation product ofepichlorohydrin and a polyamine of molecular weight greater than onemillion, sold by Rohm and Haas Company.

Primafloc C-7, a cationic flocculant, a polyvinyl imidazoline bisulfateof molecular weight greater than one million, sold by Rohm and HaasCompany in the form of a fine powder.

Hercofloc 848, a cationic flocculant, consisting of 38-42% of anacrylamide based polymer of molecular weight in excess of one millionmixed with unreacted monomer and various solvents, sold by HerculesIncorporated in the form of a liquid of viscosity 120,000-170,000centipoise at 25° C.

Hercofloc 871, a cationic flocculant, consisting of Hercofloc 848diluted to 111/2-131/2% polymer with water, a liquid with a viscosity of3300 centipoise at 24° C.

Calgon WT-2820, a cationic flocculant, a homopolymer sold by CalgonCorp. as a viscous liquid, 6% in water.

Primafloc A-10, an anionic flocculant, a copolymer of methacrylic acidand an acrylic ester, sold in the form of a 20% aqueous emulsion by Rohmand Haas Company. This material must be neutralized with base beforeuse.

Purifloc A-23, an anionic flocculant, a partially hydrolyzedpolyacrylamide of high molecular weight, sold by Dow Chemical Company inthe form of a fine powder. A specially pure grade of this material,Purifloc A-23P, is sold for use in treating potable water.

Betz 1130 polymer, an anionic flocculant, a very strongly anionic, highmolecular weight acrylamide copolymer, sold by Betz Laboratories in theform of a fine powder. It is also sold under the designations Betz 1230,1330, 1430, 2830 and 3330.

The process of this invention may be carried out at temperatures in therange of about 35° to about 200° F., preferably in the range from about60° to about 170° F., and more preferably in the range from about 100°to about 160° F. Although the flocculation and flotation of carbonaceousmaterial is most rapid at a temperature of about 160° F., it also takesplace at a highly satisfactory rate at temperatures of about 68° F. Themore rapid rate of separation at elevated temperatures is believed to bedue, at least in part, to a reduced viscosity. Operation at temperaturesabove about 160° F. is undesirable since high temperatures effect arelatively rapid reduction of the polyphosphate content of the ammoniumpolyphosphate solution.

The organic, ionic, polymeric flocculant may be mixed with the black,unclarified ammonium polyphosphate solution at a temperature which ishigher than that at which flocculation and flotation is permitted totake place. In an especially preferred embodiment, the mixing step iscarried out at a temperature from about 100° to about 200° F. andflocculation is allowed to take place at a lower temperature in therange of from about 35° to about 120° F.

Since the organic, ionic, polymeric flocculants are water soluble andare used in aqueous solution, they are easily mixed with the ammoniumpolyphosphate solutions of this invention, and very litte agitation isnecessary. The process does not require mixing in excess of that whichis produced by turbulent flow through pipes.

The cationic or anionic, polymeric organic flocculants of this inventionare used in very small quantities which may range from about 0.001 toabout 0.5% by weight based on the weight of the black ammoniumpolyphosphate solution which is undergoing treatment. Preferably, theamount of organic, ionic, polymeric flocculant is from about 0.005 toabout 0.08%, and more preferably, from about 0.01 to about 0.04% byweight based on the weight of ammonium polyphosphate solution.

In a highly preferred embodiment, the black ammonium polyphosphatesolution is first mixed with a cationic, polymeric, organic flocculantand then, subsequently, mixed with an anionic, polymeric, organicflocculant. The amount of cationic polymer is from about 0.001 to about0.5% and preferably from about 0.01 to about 0.04%, and the amount ofanionic polymer is from about 0.001 to about 0.1% and preferably fromabout 0.005 to about 0.02%, wherein said percentages are by weight andare based on the weight of the black ammonium polyphosphate solution.The ratio of cationic to anionic flocculant may range from about 100:1to about 1:10, more preferably from about 10:1 to about 1:5, and mostpreferably from about 4:1 to about 1:1. This sequential addition ofcationic flocculant followed by anionic flocculant affords highlysatisfactory flocculation at polymer addition levels which aresubstantially lower than those which are necessary when only a cationicflocculant or only an anionic flocculant is used. This synergisticeffect is not observed, however, when the cationic and anionicflocculants are added simultaneously.

In another embodiment, the black ammonium polyphosphate solution isfirst mixed with an anionic, polymeric, organic flocculant and then,subsequently, mixed with a cationic, polymeric, organic flocculant. Theamount of anionic polymer is from about 0.001 to about 0.5% andpreferably from about 0.01 to about 0.04%, and the amount of cationicpolymer is from about 0.001 to about 0.1% and preferably from about0.005 to about 0.02%, wherein said percentages are by weight and arebased on the weight of the black ammonium polyphosphate solution.

The black ammonium polyphosphate solution, after mixing with the ionic,polymeric organic flocculating agent or agents, is allowed to stand fora period of time effective to permit the separation of the mixtures intoan upper layer of flocculated carbonaceous material and a lower layer ofclarified ammonium polyphosphate solution. The period of time requiredfor satisfactory separation may range from a few minutes to severaldays. Preferably, however, the holding period is at least about onehour. After separation has taken place, the lower layer of clarifiedsolution is removed.

The entire process, or parts of it, may be carried out eithercontinuously or in a batch-type operation. The process may be carriedout continuously by pumping a mixture of black ammonium polyphosphatesolution and ionic, polymeric, organic flocculating agent or agents intoa vertical holding vessel from which clarified ammonium polyphosphatesolution is continuously removed from the bottom while flocculatedcarbonaceous material is removed from the top. This holding vessel mustbe large enough to ensure a residence time which is effective to permitthe separation of clarified liquid and flocculated carbonaceousmaterial. Removal of flocculated carbonaceous material from the top ofthe holding vessel may be accomplished by pumping means or, more simply,by allowing it to overflow into another storage vessel. Since, however,this flocculated material will be considerably thickened, mechanicalmeans such as a moving arm or buckets may be necessary to assist in itsremoval. To accelerate and further improve the flocculation andseparation, air flotation may be utilized, which involves theintroduction of air into the mixture contained in the holding vessel.

The process may also be carried out in a batch-type operation. In suchan operation, the mixture of black ammonium polyphosphate solution andionic, polymeric, organic flocculating agent or agents is collected in alarge holding vessel and allowed to stand until flocculation andseparation of the carbonaceous material is complete. The lower layer ofclarified ammonium polyphosphate solution is removed through a bottomconnection, and the upper layer of flocculated carbonaceous material isthen removed through the same connection. If the upper layer is tooviscous for easy flow, it may be mixed with some of the lower layer,which has been left behind for this purpose, thus reducing its viscosityto a manageable value. The viscosity of the upper layer of flocculatedmaterial may also be reduced by mixing it with unclarified blackammonium polyphosphate solution. Alternatively, the upper layer offlocculated material may be pumped off through a floating intake locateda short distance below the top of the mixture.

The clarified ammonium polyphosphate solutions produced by the processof this invention are suitable either for direct use as liquidfertilizers or for further processing into related fertilizers. Theclarified 10-34-0 grade ammonium polyphosphate solution preparedaccording to this process is particularly suitable for use as a liquidfertilizer.

When a 10-34-0 grade black ammonium polyphosphate solution is clarifiedaccording to the process of this invention, the upper layer offlocculated carbonaceous material, containing up to about 5% ofcoagulated material and flocculants, also analyzes as 10-34-0fertilizer. This upper layer can be used in preparing suspensionfertilizers, such as 3-10-27 grade material, either without dilution orafter dilution with clarified or unclarified 10-34-0 grade solution forease of handling. In addition, since the upper layer may contain up toabout 5% of coagulated polyelectrolyte particulates plus polyelectrolyteflocculants and in view of the fact that these materials are soilconditioners and improvers for sandy and clay soils, this upper layermaterial is valuable as a combined fertilizer and soil conditioner forsuch soils.

The following examples are intended only to illustrate the invention andare not to be construed as imposing limitations on the invention.

EXAMPLE I

The results set forth in Tables 1-9 were obtained by mixing preheated200 g. portions of a black 10-34-0 grade ammonium polyphosphate solutionwith aqueous solutions of various flocculants in a one pint WaringBlender for 30 seconds. Each resulting mixture was then poured into a125 ml. graduated, cylindrical separatory funnel and held at acontrolled temperature. The efficiency of the various flocculants incausing the suspended, black carbonaceous material to coagulate andseparate as an upper layer was determined by measuring the percentage ofclarified liquid present as a lower layer in the separatory funnelsafter 5, 10, 30 and 60 minutes. The presence of either large particlesof flocculated material or of small specks suspended in the otherwiseclear lower layer was also noted. At the end of 60 minutes, a sample ofthe clarified lower layer was drained into a spectrophotometer cell andits absorbance measured at 560 nm using a Beckman DB-GT double beamgrating instrument with distilled water as the reference.

In those runs wherein a sequential addition of two different flocculantswas employed, the first flocculant was added according to the abovedescribed general procedure. After a selected period of time, the secondflocculant was added in the form of an aqueous solution and mixed for 30seconds in the Waring Blender. This final mixture was then poured into agraduated, cylindrical separatory funnel and observations made asdescribed above.

The results set forth in Table 1 serve to demonstrate that the cationicflocculants are more effective at low concentrations than are theanionic flocculants.

The results set forth in Table 2 indicate that the simultaneous additionof equal amounts by weight of both cationic and anionic polymericorganic flocculants is substantially ineffective in clarifying blackammonium polyphosphate solutions.

The results of Tables 1 and 3 demonstrate that substantially improvedresults are obtained by the sequential addition of cationic and anionicflocculants as opposed to the use of an equivalent amount of only asingle cationic or anionic flocculant.

The series of tests set forth in Table 4 demonstrates that veryeffective flocculation can be produced through the use of Primafloc C-7followed by either Primafloc A-10 or Purifloc A-23. There is very littlechange on extending the time between additions from 2 to 10 minutes,although the results of Table 2 indicate that some time interval betweenadditions is essential. Table 4 also shows that the rate of flocculantsis important. A ratio of cationic flocculant to anionic flocculant of1:2 is clearly inferior to a ratio of 2:1.

Table 5 serves to supplement Table 4 and demonstrates that improvedresults are obtained with larger amounts of flocculants.

The results set forth in Table 6 indicate that flocculation andseparation of the carbonaceous material as an upper layer is improved byraising the temperature to 160° F., but a further increase to 190° F.serves to inhibit the separation. Table 6 shows that excellentseparations can be obtained at 160° F. while using much less flocculantthan is needed at 68° F.

The results set forth in Tables 7 and 8 show that the temperature ofinitial mixing is more important than the temperature at which themixture is held for flocculation and separation. With a mixingtemperature of 160° to 190° F., fair separations can be obtained with0.01% of Primafloc C-7 alone, and good separations can be obtained with0.02% if the mixtures are held at 68° F. subsequent to mixing.

Runs 1 and 8-10 in Table 9 serve to illustrate the use of additionalionic, polymeric organic flocculants which may be used in the process ofthis invention. The negative results of Runs 2-7 are representative ofthe results which are obtained with most conventional flocculants.

EXAMPLE II

The results set forth in Table 10 were obtained by continuously adding a2% aqueous solution of Primafloc C-7 to a fresh 140° F. stream of black10-34-0 ammonium polyphosphate solution from a pipe reactor. The mixturewent through a cooler and then through a holding tank. After a totalholding time of about 12 minutes, the stream, now cooled to 105° F., wasmixed with 1% aqueous Primafloc A-10 and run into a storage tank havinga height and diameter of 12 feet. This process was continued until thestorage tank was filled, usually in about seven hours. Samples weretaken before and after the A-10 addition point, poured into separatoryfunnels and examined as before. The separation in the tank was alsomeasured at intervals of up to two weeks. The production rate of 10-34-0solution varied from 19 to 30 gallons per minute during these runs.

The clear green lower phase obtained in Run 2A was analyzed and found tobe of high quality and possessed a polyphosphate content equal to thatof the black 10-34-0 starting material. The black upper layer ofcoagulated carbonaceous material from Run 2A was mixed with enough ofthe clarified lower layer to reduce its viscosity and was thenformulated into a 3-10-27 grade fertilizer, which was as good as 3-10-27fertilizer made from untreated black 10-34-0 ammonium polyphosphatesolution.

                                      TABLE 1.                                    __________________________________________________________________________    Addition of 2% Aqueous Solutions of Single Flocculants,                       Starting at 68° F. and Holding at 68° F.                                    Weight of                                                                     Flocculant                                                                           % Lower Layer Separated After                                          Solution                                                                             5    10   30   60     Absorbance                           Run Flocculant                                                                            Added (g.)                                                                           Minutes                                                                            Minutes                                                                            Minutes                                                                            Minutes                                                                              at 560 nm                            __________________________________________________________________________    1   Primafloc C-3                                                                         1.00   0    0    0    29, semi-clear                                                                       1.92                                 2   Primafloc C-3                                                                         0.100  0    0    0    0                                           3   Primafloc C-7                                                                         1.00   0    0    0    25, semi-clear                                                                       1.82                                 4   Primafloc C-7                                                                         0.100  0    0    0    0                                           5   Purifloc A-23                                                                         1.00   0    0    0    0                                           6   Purifloc A-23                                                                         0.100  0    0    0    0                                           7   Primafloc A-10                                                                        1.00   0    0    0    0                                           8   Primafloc A-10                                                                        0.100  0    0    0    0                                           __________________________________________________________________________

                                      TABLE 2.                                    __________________________________________________________________________    Simultaneous Addition of 2% Aqueous Solutions of Two Flocculants,             Starting at 68° F. and Holding at 68° F.                                  g. of                                                                         Each         % Lower Layer Separated After                             First  Soln.                                                                              Second  5    10   30   60   Absorbance -Run Flocculant Adde                                               d Flocculant Minutes Minutes Mi                                               nutes Minutes at 560               __________________________________________________________________________                                               nm                                 1  Primafloc C-3                                                                        1.00 Purifloc A-23                                                                         0    0    0    5    --                                 2  Primafloc C-3                                                                        0.100                                                                              Purifloc A-23                                                                         0    0    0    2    --                                 3  Primafloc C-3                                                                        1.00 Primafloc A-10                                                                        0    0    0    1    --                                 4  Primafloc C-3                                                                        0.100                                                                              Primafloc A-10                                                                        0    0    0    1    --                                 5  Primafloc C-7                                                                        1.00 Purifloc A-23                                                                         0    1    2    5    --                                 6  Primafloc C-7                                                                        0.100                                                                              Purifloc A-23                                                                         0    0    0    1    --                                 7  Primafloc C-7                                                                        1.00 Primafloc A-10                                                                        0    0    2    5    1.92                               8  Primafloc C-7                                                                        0.100                                                                              Primafloc A-10                                                                        0    0    0    0    --                                 __________________________________________________________________________

                                      TABLE 3.                                    __________________________________________________________________________    Addition of a 2% Aqueous Solution of a Cationic Flocculant Followed,          After 5 Minutes, by the Addition of a 2% Aqueous Solution of an               Anionic Flocculant, Starting at 68° F. and Holding at 68°       F.                                                                                      g. of                                                                         Each         % Lower Layer Separated After                             First  Soln.                                                                              Second  5    10   30   60   Absorbance at                      Run                                                                              Flocculant                                                                           Added                                                                              Flocculant                                                                            Minutes                                                                            Minutes                                                                            Minutes                                                                            Minutes                                                                            560 nm                             __________________________________________________________________________    1  Primafloc C-3                                                                        1.00 Purifloc A-23                                                                         0    0    7    15   >3                                 2  Primafloc C-3                                                                        0.100                                                                              Purifloc A-23                                                                         0    0    0    1    --                                 3  Primafloc C-3                                                                        1.00 Primafloc A-10                                                                        0    0.5  1    35   >3                                 4  Primafloc C-3                                                                        0.100                                                                              Primafloc A-10                                                                        0    0    1    3    --                                 5  Primafloc C-7                                                                        1.00 Purifloc A-23                                                                         0    1    1.5  65   1.08                               6  Primafloc C-7                                                                        0.100                                                                              Purifloc A-23                                                                         0    0    1    1    --                                 7  Primafloc C-7                                                                        1.00 Primafloc A-10                                                                        0    0    1.5  55   1.66                               8  Primafloc C-7                                                                        0.100                                                                              Primafloc A-10                                                                        0    0    1    5    >3                                 __________________________________________________________________________

                                      TABLE 4.                                    __________________________________________________________________________    Addition of 2% Aqueous Primafloc C-7 Followed by the Addition of              a 2% Aqueous Solution of an Anionic Flocculant, Starting at 68°        F.                                                                            and Holding at 68° F.                                                  g. of 2%                                                                      Primafloc                                                                              Minutes      g. of                                                                             % Lower Layer Separated After                          C-7   Between                                                                            Second  Soln.                                                                             5    10   30   60   Absorbance at                   Run                                                                              Added Additions                                                                          Flocculant                                                                            Added                                                                             Minutes                                                                            Minutes                                                                            Minutes                                                                            Minutes                                                                            560 nm                          __________________________________________________________________________    1  1.00  2    Purifloc A-23                                                                         0.50                                                                              5    5    15   18   1.61                            2  1.00  2    Purifloc A-23                                                                         2.00                                                                              5    5    5    14   1.31                            3  0.50  2    Purifloc A-23                                                                         1.00                                                                              3    4    5    6    1.53                            4  2.00  2    Purifloc A-23                                                                         1.00                                                                              1    10   22   42   0.90                            5  1.00  2    Primafloc A-10                                                                        0.50                                                                              3    3    14   27   1.08                            6  1.00  2    Primafloc A-10                                                                        2.00                                                                              4    5    21   27   1.37                            7  0.50  2    Primafloc A-10                                                                        1.00                                                                              4    5    5    8    >2                              8  2.00  2    Primafloc A-10                                                                        1.00                                                                              5    8    27   52   0.67                            9  1.00  5    Purifloc A-23                                                                         0.50                                                                              0    1    7    12   1.58                            10 1.00  5    Purifloc A-23                                                                         2.00                                                                              0    1/2  1    9    1.48                            11 0.50  5    Purifloc A-23                                                                         1.00                                                                              0    0    1/2  1    >2                              12 2.00  5    Purifloc A-23                                                                         1.00                                                                              2    2    30   50   0.86                            13 1.00  5    Primafloc A-10                                                                        0.50                                                                              1    1    8    15   1.72                            14 1.00  5    Primafloc A-10                                                                        2.00                                                                              0    1    15   19   1.37                            15 0.50  5    Primafloc A-10                                                                        1.00                                                                              0    0    1    2    >2                              16 2.00  5    Primafloc A-10                                                                        1.00                                                                              1    1    26   48   0.58                            17 1.00  10   Purifloc A-23                                                                         0.50                                                                              3    4    13   14   1.21                            18 1.00  10   Purifloc A-23                                                                         2.00                                                                              0    0    2    4    >2                              19 0.50  10   Purifloc A-23                                                                         1.00                                                                              2    4    5    5    >2                              20 2.00  10   Purifloc A-23                                                                         1.00                                                                              3    5    37   57   0.81                            21 1.00  10   Primafloc A-10                                                                        0.50                                                                              2    3    4    17   >2                              22 1.00  10   Primafloc A-10                                                                        2.00                                                                              0    0    4    14   1.38                            23 0.50  10   Primafloc A-10                                                                        1.00                                                                              0    0    1    1    >2                              24 2.00  10   Primafloc A-10                                                                        1.00                                                                              0    1    30   47   0.65                            __________________________________________________________________________

                                      TABLE 5.                                    __________________________________________________________________________    Addition of 2% Aqueous Primafloc C-7 Followed, After 5 Minutes,               by the Addition of a 2% Aqueous Solution of an Anionic Flocculant,            Starting at 68° F. and Holding at 68° F.                        g. of 2%                                                                      Aqueous         g. of 2%                                                      C-7     Second  Flocculant                                                                          % Lower Layer Separated After      Absorbance           Run                                                                              Added                                                                              Flocculant                                                                            Added 5 Minutes                                                                              10 Minutes                                                                             30 Minutes                                                                             60 Minutes                                                                            at 560               __________________________________________________________________________                                                             nm                   1  4.0  Primafloc A-10                                                                        1.0   1        25       60       67-black                                                                              0.54ks               2  4.0  Primafloc A-10                                                                        2.0   13       24       60       70-black                                                                              0.89ks               3  4.0  Purifloc A-23                                                                         1.0   3        24       51-black specks                                                                        60-black                                                                              0.45ks               4  4.0  Purifloc A-23                                                                         2.0   10-black specks                                                                        20-black specks                                                                        50-black specks                                                                        64-black                                                                              0.52ks               5  4.0  Purifloc A-23                                                                         0.5   2        18-black specks                                                                        46-black specks                                                                        60-black                                                                              0.41ks               6  4.0  Primafloc A-10                                                                        0.5   5        38-black specks                                                                        66-black specks                                                                        75-black                                                                              0.88ks               7  2.0  Purifloc A-23                                                                         0.5   1        1        10-black specks                                                                        15-black                                                                              0.90ks               8  2.0  Primafloc A-10                                                                        0.5   0        0        15-black specks                                                                        20-black                                                                              1.31ks               9  1.0  Purifloc A-23                                                                         1.0   0        1        1        1       >2                   10 1.0  Primafloc A-10                                                                        1.0   0        1        5-black specks                                                                         10-black                                                                              1.85ks               11 2.0  Purifloc A-23                                                                         1.0   0        1        16-black specks                                                                        37-black                                                                              0.55ks               12 2.0  Primafloc A-10                                                                        1.0   0        0        15-black specks                                                                        30-black                                                                              1.28ks               13 2.0  Primafloc A-10                                                                        2.0   1        10-black specks                                                                        26-black specks                                                                        47-black                                                                              1.04ks               14 4.0  None    0     1        45-black flocks                                                                        75-black specks                                                                        81-black                                                                              0.88ks               __________________________________________________________________________

                                      TABLE 6.                                    __________________________________________________________________________    Addition of 2% Aqueous Primafloc C-7 Followed, After 5 Minutes,               by the Addition of a 2% Aqueous Solution of an Anionic Flocculant,            Starting at an Elevated Temperature and Holding at the Same Temperature.      g. of 2%         g. of 2%                                  Ab-                Aqueous          Aqueous                                   sor-               Primafloc        Second                                    bance              C-7      Second  Flocculant                                                                          Temp.                                                                             % Lower Layer Separated After   at                 Run                                                                              Added Flocculant                                                                            Added (°F.)                                                                      5 Minutes                                                                             10 Minutes                                                                            30 Minutes                                                                            60 Minutes                                                                            560                __________________________________________________________________________                                                               nm                 1  2.0   Primafloc A-10                                                                        1.0   160 30-black flocks                                                                       68-black specks                                                                       75-black specks                                                                       78-black                                                                              0.44ks             2  2.0   Purifloc A-23                                                                         1.0   160 62-black flocks                                                                       72-black specks                                                                       75-black specks                                                                       75-black                                                                              0.56ks             3  4.0   None    0     160 37-black flocks                                                                       45-black specks                                                                       55-black specks                                                                       63      0.33               4  1.0   Primafloc A-10                                                                        1.0   160 0       0       0       1/2     --                 5  1.0   Purifloc A-23                                                                         1.0   160 0       0       1       0       --                 6  3.0   Primafloc A-10                                                                        1.0   160 55-black flocks                                                                       62-black specks                                                                       67-black specks                                                                       82-black                                                                              0.53ks             7  3.0   Purifloc A-23                                                                         1.0   160 50-black specks                                                                       63-black specks                                                                       68-black specks                                                                       69-black                                                                              0.53ks             8  3.0   None    --    160 73-black specks                                                                       83-black specks                                                                       82-black specks                                                                       86      0.37               9  2.0   Primafloc A-10                                                                        1.0   190 0       0       12-black flocks                                                                       42-black                                                                              >2ocks             10 2.0   Purifloc A-23                                                                         1.0   190 0       0       15-black flocks                                                                       50-black                                                                              1.58ks             11 2.0   Purifloc A-23                                                                         0.5   160 24-black flocks                                                                       60-black specks                                                                       71-black specks                                                                       75      0.49               12 2.0   Primafloc A-10                                                                        0.5   160 55-black flocks                                                                       66-black specks                                                                       78      80      0.51               13 1.0   Purifloc A-23                                                                         0.5   160 0       2       25-black specks                                                                       60-black                                                                              0.99ks             14 1.0   Primafloc A-10                                                                        0.5   160 17-black flocks                                                                       42-black flocks                                                                       61-black specks                                                                       75-black                                                                              0.56ks             15 2.0   None    0     160 45-black flocks                                                                       65-black flocks                                                                       70-black specks                                                                       73-black                                                                              0.31ks             16 1.0   None    0     160 15-black flocks                                                                       45-black flocks                                                                       67-black flocks                                                                       75-black                                                                              0.39ks             17 None  None    0     160 0       0       0       0       >2                 18 0.5   None    0     160 0       15-black flocks                                                                       55-black flocks                                                                       66-black                                                                              0.80ks             19 None  Purifloc A-23                                                                         2.0   160 0       0       0       0       >2                 20 None  Purifloc A-23                                                                         1.0   160 0       0       0       0       >2                 21 None  Primafloc A-10                                                                        2.0   160 0       0       0       0       >2                 22 None  Primafloc A-10                                                                        1.0   160 0       0       0       0       >2                 23  0.25 None    0     160 0       0       12-black specks                                                                       35-black                                                                              >2ocks             __________________________________________________________________________

                                      TABLE 7.                                    __________________________________________________________________________    Addition of 2% Aqueous Primafloc C-7, Starting at an Elevated                 Temperature, Pouring Into a Separatory Funnel, Immediately                    Plunging Into a 68° F. Water Bath for 5 Minutes and Holding in         Air at 68° F.                                                          g. of 2%                                                                      Aqueous  Initial                                                              Primafloc                                                                              Temp.                                                                             % Lower Layer Separated After   Absorbance                       Run                                                                              C-7 Added                                                                           (°F.)                                                                      5 Minutes                                                                             10 Minutes                                                                            30 Minutes                                                                            60 Minutes                                                                            at 560 nm                        __________________________________________________________________________    1  2.0   160 5       15-black flocks                                                                       43-black flocks                                                                       55-black flocks                                                                       0.44                             2  2.0   190 10-black flocks                                                                       47-black flocks                                                                       60-black specks                                                                       65-black specks                                                                       0.41                             3  1.0   160 0       1-black flock                                                                         15-black flocks                                                                       30-black flocks                                                                       1.06                             4  1.0   190 0       1-black flock                                                                         30-black flocks                                                                       55-black flocks                                                                       1.42                             __________________________________________________________________________

                                      TABLE 8.                                    __________________________________________________________________________    Addition of 2% Aqueous Primafloc C-7, Starting at 140° F.              and Holding at 105° F. in a Water Bath.                                          g. of 2%       g. of 2%                                                       Aqueous        Aqueous                                              First     First Second   Second                                                                              % Lower Layer Separated After                                                                     Absorbance                 Run                                                                              Flocculant                                                                           Flocculant                                                                          Flocculant                                                                             Flocculant                                                                          5 Min.                                                                             10 Min.                                                                            30 Min.                                                                            60 Min.                                                                            at 560                     __________________________________________________________________________                                                       nm                         1  Primafloc C-7                                                                        2.0   Primafloc A-10.sup.(a)                                                                 1.0   10-flocks                                                                          22-flocks                                                                          55-specks                                                                          65-specks                                                                          0.88                       2  Primafloc C-7                                                                        1.5   None     0      5-flocks                                                                          10-specks                                                                          30-specks                                                                          45-specks                                                                          1.68                       3  Primafloc C-7                                                                        2.0   None     0      5-specks                                                                          21-flocks                                                                          59-specks                                                                          66-specks                                                                          0.45                       4  Primafloc C-7                                                                        3.0   None     0     30-flocks                                                                          55-specks                                                                          73-specks                                                                          76-specks                                                                          0.45                       5  Primafloc C-7                                                                        4.0   None     0     15-flocks                                                                          70-flocks                                                                          78-flocks                                                                          80-specks                                                                          1.05                       __________________________________________________________________________     .sup.(a) 2% aqueous solution of Primafloc A10 added 5 minutes after the       initial addition of Primafloc C7.?                                       

                                      TABLE 9.                                    __________________________________________________________________________    Addition of Single Flocculants, Starting at 140° F. and                Holding at 105° F. in a Water Bath                                                       Amount                                                                        Flocculant                                                                             % Lower Layer Separated After                                                                         Absorbance                 Run                                                                              Flocculant     Added    5 Minutes                                                                           10 Minutes                                                                          30 Minutes                                                                          60 Minutes                                                                          at 560                     __________________________________________________________________________                                                       nm                         1  Calgon WT-2820 (6% Active)                                                                   0.67 g.  48-flocks                                                                           65-flocks                                                                           75-flocks                                                                           78-specks                                                                           0.38                       2  Dow Purifloc C-41                                                                            2 g. 2% Aq. Soln.                                                                      0     0     0     0     >2                         3  Dearborn X-1807                                                                              2 g. 2% Aq. Soln.                                                                      0     0     0     0     >2                         4  Dearborn 4891  2 g. 2% Aq. Soln.                                                                      0     0     0     0     >2                         5  Dearborn Aquafloc 431                                                                        2 g. 2% Aq. Soln.                                                                      0     0     0     0     >2                         6  Dearborn Aquafloc 420                                                                        2 g. 2% Aq. Soln.                                                                      0     0     0     0     >2                         7  Dearborn Aquafloc 417                                                                        2 g. 2% Aq. Soln.                                                                      0     0     0     0     >2                         8  Hercofloc 871  0.13 g.  10-flocks                                                                           25-flocks                                                                           55-specks                                                                           65-specks                                                                           1.02                          (111/2-131/2% Active)                                                      9  Hercofloc 848  2 g. 2% Aq. Soln.                                                                      5-flocks                                                                            17-flocks                                                                           37-flocks                                                                           52-specks                                                                           1.75                          (38- 42% Active)                                                           10 Betz 1130      2 g. 2% Aq. Soln.                                                                      0     5-flocks                                                                            15-flocks                                                                           60-flocks                                                                           2.51                       __________________________________________________________________________

                  TABLE 10.                                                       ______________________________________                                        Large Scale Clarification of Black 10-34-0 Grade                              Ammonium Polyphosphate Solutions.                                                                   Time   %                                                     % C-7   % A-10   After  Clear  Lower                                          in      in       Last   Lower  Phase Absorbance                          Run  10-34-0 10-34-0  Addition                                                                             Phase  at 560 nm                                 ______________________________________                                        1 A  0.027   0        60  Min. 72-specks                                                                            0.60                                    1 B  0.027   0.013    60  Min. 81-specks                                                                            0.28                                                          6   Days 95     0.17                                    2 A  0.020   0.0057   60  Min. 67-specks                                                                            0.35                                                          1   Day  83     0.26                                                          3   Days 91     0.12                                    2 B  0.020   0        60  Min. 64-specks                                                                            0.98                                    3    0.026   0        60  Min. 61-specks                                                                            0.50                                                          12  Days 91                                             ______________________________________                                    

I claim:
 1. A process for the removal of suspended carbonaceous materialfrom an aqueous ammonium polyphosphate solution wherein (i) saidsolution contains from about 10 to about 90% by weight of the total P₂O₅ in a polyphosphate form, (ii) said solution has a pH above about 4.5,(iii) said solution is prepared by the molecular dehydration andsubsequent or concurrent ammoniation of wet-process phosphoric acid,(iv) said solution ranges in grade from about 8-27-0 to about 13-37-0,and (v) said carbonaceous material results from organic impurities insaid wet-process phosphoric acid which char during said moleculardehydration, which process comprises the steps of:(a) mixing saidammonium polyphosphate solution with an aqueous solution of a polyvinylimidazoline bisulfate having a high charge density and a molecularweight in excess of one million, wherein the amount of said polyvinylimidazoline bisulfate is from about 0.001 to about 0.5% by weight basedon the weight of said ammonium polyphosphate solution, and wherein saidaqueous polyvinyl imidazoline bisulfate solution contains from about 0.1to about 5% by weight of said polyvinyl imidazoline bisulfate; (b)holding the resulting mixture for a period of time effective to permitthe separation of said mixture into an upper layer of flocculatedcarbonaceous material and a lower layer of clarified ammoniumpolyphosphate solution; and (c) separating said lower layer of clarifiedammonium polyphosphate solution from said upper layer of flocculatedcarbonaceous material.
 2. The process as set forth in claim 1 wherein anaqueous solution of at least one anionic polymer having a high chargedensity and a molecular weight in excess of one million is additionallyadded to said mixture of ammonium polyphosphate solution and aqueouspolyvinyl imidazoline bisulfate solution, wherein said anionic polymeris a copolymer of methacrylic acid and an acrylic ester which has beenneutralized with base, wherein the amount of said anionic polymer isfrom about 0.001 to about 0.1% by weight based on the weight of saidammonium polyphosphate solution, wherein said aqueous anionic polymersolution contains from about 0.1 to about 5% by weight of said anionicpolymer, and wherein said anionic polymer is added to the ammoniumpolyphosphate solution subsequent to the addition of said polyvinylimidazoline bisulfate.